Asexual and Sexual Reproduction
• Genetically identical cells are produced from a single parent cell by mitosis. Fission or Budding
• Sexual reproduction occurs when new individual is formed through union of two sex cells (gametes). Produce zygote. Haploid gametes formed by meiosis in sex
organs (gonads).
Asexual and Sexual Reproduction
• Different Approaches to Sex Parthogenesis - Virgin birth
- Exclusive- Switching
Sexual Reproduction- monoecious / dioecious- Hermaphroditism - Both Sex organs
Evolution of Reproduction
• Three Strategies of Internal Fertilization: Oviparity - Eggs are fertilized internally and
deposited outside mother’s body to complete development.
Ovoviviparity - Fertilized eggs are retained within mother to complete development, but all nourishment gained from yolk sac.
Viviparity - Young develop within mother and obtain nourishment directly from mother’s blood.
Porifera and Cnidaria
• Sponges reproduce by both asexual and sexual means. Most poriferans that reproduce by sexual means are hermaphroditic and produce eggs and sperm at different times.
• Cnidarians reproduce by both asexual and sexual means.
Arthropoda
• reproduction dioecious - many dimorphic oviparous, or ovoviviparous metamorphosis - complete / incomplete some parthenogenic – development from a
unfertilized ovum.- Fertilization can be internal- males have an
ovipositor
Annelida
• reproduction monoecious / dioecious trochophore larva asexual - budding Fertilization external Gametes passed into the coelom (body cavity)
Evolution of Vertebrate Reproduction
• Vertebrate sexual reproduction evolved in the ocean before vertebrates colonized land.
Most marine bony fish utilize external fertilization. Most other vertebrates utilize internal
fertilization.- Gametes could not be released on dry
land without significant mortality.
Sexual Reproduction
• Sex Determination In some organisms, environmental
conditions can determine sex of offspring.- In mammals, sex is determined early in
embryonic development. Embryonic gonads are indifferent.
Y chromosome produce males.
Animals: Sex Determination
Plant Life Cycle
Alternation of generations
Alternation of generations in Gynosperms
Alternation of generations in angiosperms
Comparison between Animal and Plant life cycles
• Plants gametes divide so individuals are haploid or diploid
• Animals individuals • are diploid and
gametes are haploid